High and low-pressure laminates are well known and typically include a paper sheet secured to a substrate such as a wafer board, chipboard, plywood or particle board to form a laminate. The sheet bears a decorative design, such as an attractive wood grain applied to a print surface of the sheet. The sheet is next impregnated with a thermosetting resin and then thermally fused to the substrate under heat and pressure to form the laminate. The laminate is then cut into well known decorative boards that are used as components of kitchen and bath cabinets, office furniture, recreational furniture, store fixtures, etc. Low-pressure laminates wherein the impregnated sheet is secured directly to the substrate at temperatures ranging from 325–385 degrees Fahrenheit (hereafter “° F.”) and at pressures between about 175–325 pounds per square inch (hereafter “p.s.i.”), have replaced more costly high-pressure laminates for many purposes.
Many efforts have been undertaken over the years to improve the appearance of such low pressure and multi-layer high-pressure decorative boards by, for example, generating a textural look on the print surface of the sheet and/or of the resulting laminate decorative board. Such efforts include mechanical embossing by application under pressure of metal plates to a layer of the boards wherein the steel plates have a desired wood-grain texture cut into a surface of the plates. This of course involves great expense in producing the plates, and great difficulty in applying the plates with accuracy of alignment to a layer of the board. Non-mechanically embossed laminates have also been produced by use of chemical embossing. For example, a printing ink containing a chemical substance that inhibits curing of the thermosetting resin may be secured to a base layer of the laminate with the ink. Then, the uncured resin may be removed from the laminate leaving recessed portions of the decorative board. Removal of the uncured resin, however is also a costly undertaking.
Another non-mechanical embossing method is shown in U.S. Pat. No. 5,779,840 to Boris wherein a wood-grain “tick” pattern results from removal of a carrier sheet that had been adhered to spaced apart markings of the tick pattern on the laminate. Because such laminate based decorative boards are covered with a cured protective resin, to effectively generate a wood-grain appearance, the surface of the boards must either show non-planar indentations or a gloss differential at the surface of the board. The inks used in Boris have varying gloss characteristics, and the removal of the carrier layer results in a gloss differential between the inks. U.S. Pat. No. 4,971,854 to Hinishi et al. similarly uses a detaching release layer after heating and pressing a thermoset resin impregnated laminate to produce an appearance of wood-grain texture.
In U.S. Pat. No. 6,551,694 to Imamichi et al., another non-mechanical embossing method is disclosed, wherein a first ink covering an ordinary pattern and a second, liquid repellant ink covering a second pattern are applied to a base layer of a sheet. A thermosetting resin that is repelled by the liquid repellant in the ink is then applied, and upon curing, recessed portions of a surface of the decorative board are produced over the portions of the base layer that had the liquid repellant ink. While producing a texture-like appearance, the decorative board of Imamichi et al. requires costly application of complicated inks and requires use of special thermosetting resins. Moreover, the contours and dimensions of the recessed portions are significantly limited to a narrow range dependant upon the physical characteristics of the special resins.
Accordingly, there is a need for a laminate that provides for an embossed appearance without the difficult use of costly mechanical embossing plates or complicated chemical processes, and that can be manufactured efficiently at relatively low cost.